This invention relates to an apparatus for reliably fetching data, on the basis of a framing code detection process, and a method therefor and, more particularly, to an apparatus and a method, for use in a teletext receiver, for detecting a packet-synchronizing framing code added to a start portion of each packet of a coded information signal, and for stabilizing a reference signal used to fetch a data signal following the framing code.
In a conventional code-transmission type teletext system, a coded teletext signal superposed within a vertical blanking period of a television signal is restored at the receiver side. For this reason, a synchronizing component is added to the start portion of the teletext signal. The synchronizing component is an 8-bit framing code (FC) for synchronizing the subsequent packet (information component).
The framing code (FC) represents the start of transmission of the subsequent information data (i.e., a data packet). In order to properly fetch information and achieve accurate packet synchronization, the framing code (FC) must be accurately detected. For this purpose, a specific pattern "11100101" is employed as the framing code (FC). This is because the framing code can be accurately detected even if an error occurs in the specific pattern. The specific code aims at setting an accurate minimum code length between the adjacent framing codes to be "3".
A one-bit error-correction function is assigned to the framing code (FC), and, as a result, more accurate packet (frame) synchronization can be achieved. In addition, fetching of information data can be expected to be performed more reliably.
In practice, in order to fetch information data, various reference signals must be generated on the basis of the detection results of framing codes (FC).
The one-bit error-correction function of the framing code (FC), however, adversely affects the process of setting of these reference signals. More specifically, no problem arises even when a one-bit error occurs and the framing code is then detected in this state. When a framing code is detected as the correct framing code at a timing deviating by one bit from the correct timing, according to the one-bit error-correction function, various reference signals for fetching the subsequent data cannot then be accurately set.
As described above, in a conventional teletext receiver for generating various reference signals on the basis of the framing detection results, the reference signals used for accurately fetching information data cannot be accurately set. As a result, the teletext signals cannot be reliably fetched.